Aquatic Conservation: Marine and Freshwater Ecosystems

The white shark Carcharodon carcharias (Linnaeus, 1758) is one of the most iconic and threatened marine predators globally and is listed as critically endangered by the IUCN in the Mediterranean Sea, where populations are primarily affected by fishing pressure and the degradation of critical habitats. Available information on Mediterranean white sharks mostly relies on fishing interactions and opportunistic surface records, thereby limiting evaluations on the species ecology. Here, we report an exceptionally rare underwater encounter with this species, documented by divers involved in an expedition aimed at removing ghost fishing gear from a World War II shipwreck in the Strait of Sicily (SoS), central Mediterranean. Given the exceptional nature of this observation, we analysed the video footage in detail with the aim of providing morphological information and novel insights into the species ecology. The footage analysis also allowed close observations on behavioural aspects and on interspecific and parasitic associations, thus providing information that is rarely achievable through surface sightings or from captured individuals, which historically represent the majority of records for this species in the region. To contextualize this observation within the SoS--an area suggested to function as a nursery and reproductive ground for the species--we also provide an updated compilation of records reported in the scientific literature over the last decade, adding 18 new records to existing datasets. This study highlights the value of shipwrecks as observation sites for rare and elusive species, and underscores the importance of non-invasive, video-based approaches in advancing knowledge of a species whose ecology in the Mediterranean remains poorly understood.

Small-scale fisheries provide essential coastal livelihoods in developing regions, yet they often confront severe institutional voids within fragile-state contexts. Adopting a social-ecological systems framework, this study addresses three sequential objectives: characterizing the contemporary institutional and demographic status of fishery cooperatives across the five South-Central Federal Member States in comparison to their late-1980s historical peak; ranking the socio-economic, infrastructural, regulatory, and environmental impediments to cooperative efficacy; and evaluating the contributions of these cooperatives to sustainable fisheries development. This investigation analyzes how fishery cooperatives act as institutional intermediaries to bolster economic resilience within the Somali coastal economy--a sector central to the National Transformation Plan, despite persistent regulatory fragmentation. Through semi-structured qualitative interviews with key informants--analyzed via reflexive thematic analysis and chi-square testing of age-cohort structure--the study finds that illegal, unreported, and unregulated fishing and inadequate post-harvest infrastructure are the principal constraints, whereas training, education, and community collaboration constitute the primary contributions. The results characterize these cooperatives as hybrid institutions that compensate for limited central-state capacity in remote coastal settlements while serving as intermediaries for the Federal Ministry of Fisheries and Blue Economy where co-management mandates are implemented. By extending the actor-community dimension of the SES framework to include age-cohort structure, this research demonstrates that clan-based reciprocal arrangements can serve as functional substitutes for Ostroms first design principle in contexts of persistent fragility. The study recommends multi-stakeholder partnerships to advance targeted capacity-building, financial literacy, and technological integration, and suggests future research into the post-harvest and retail sectors to examine the role of women in the Somali blue economy.

The moonfish Mene maculata (Bloch and Schneider, 1801), the sole extant species of the family Menidae, is widely distributed in the Indo-West Pacific. Although its spawning season has previously been inferred from seasonal variation in the gonadosomatic index (GSI), the histological basis for interpreting GSI as an indicator of spawning-capable status remains limited. Here we describe the gonadal structure of male and female M. maculata and evaluate how GSI and standard length relate to spawning-capable status based on germ cell development. The testis was lobular and exhibited an unrestricted spermatogonial distribution, a structure widely observed among neoteleosts, indicating that the phylogenetic distinctiveness of M. maculata was not associated with a distinctive testicular structure. In the spawning-capable female, oocytes at multiple developmental stages, from primary growth to oocyte maturation, co-occurred within the ovary, indicating asynchronous ovarian development. This finding suggests that M. maculata may be a batch spawner rather than a total spawner as previously inferred. The spawning-capable female had a GSI consistent with previously inferred spawning season estimates. By contrast, histologically examined males were spawning capable at GSI values lower than those previously associated with the inferred spawning season, suggesting that male spawning-capable status may persist beyond the period inferred from elevated GSI alone. This study provides the first histological description of reproductive biology in the phylogenetically distinctive M. maculata and establishes a histological basis for interpreting GSI as a reproductive indicator.

Blue Economy models position aquaculture as a key pathway to securing global food security. Species selected for aquaculture typically show rapid growth, high stress tolerance and fast biomass accumulation, but these same traits may increase their potential to become invasive when introduced beyond their native range. We investigated the invasion history and current status of the commercially important red seaweed Kappaphycus alvarezii in the Palk Bay-Gulf of Mannar region of India. This is one of the worlds largest cultivation hubs, a climatically vulnerable marine biodiversity hotspot, and one of the three regions to report invasion. We combined in-water surveys, interviews with wild seaweed collectors, and a review of published literature to reconstruct the history of invasion and assess current status. Invasion has declined substantially, with interviews indicating that the disappearance of invasive populations began around 2014. We discuss several non-mutually exclusive explanations for this decline, including climate change, loss of coral substrate, herbivory, and reduced vitality of the seaweed. Although the decline in invasion is encouraging for coral reefs, our findings raise questions about the ecological and socioeconomic consequences of introducing non-native aquaculture species under Blue Economy initiatives, particularly in ecologically sensitive regions vulnerable to climate change.

The non-indigenous brown macroalga Rugulopteryx okamurae has emerged as one of the most aggressive marine invaders in European waters, deeply altering benthic communities and causing severe socioeconomic impacts. While its expansion has been extensively documented along the southern Iberian Peninsula, understanding the dynamics of its northward range expansion along the Spanish Mediterranean coast remains critical for coastal management. This study documents the first formal record of R. okamurae in Calpe (Alicante), representing its current northernmost distribution limit within the Comunitat Valenciana. Sampling was conducted through an initial opportunistic scuba diving observation along the surrounding waters of the Penyal dIfac Natural Park, followed by targeted underwater surveys and an ad hoc inspection of commercial bottom-trawling nets drying at the port of Calpe during June 2026. Morphological and anatomical identification was confirmed through cross-sections of the thallus under optical microscopy, revealing the presence of both the thick and intermediate morphotypes of the species. The collected specimens were found either entangled within a native photophilic algal canopy in shallow waters or recovered from deeper offshore fishing grounds. Given the absence of records in the area during 2023-2025 surveys, these findings suggest either a very recent front-wave colonization event or a contribution from nearby, yet undetected, established patches, driven by secondary local dispersal mechanisms such as drifting fragments and explicitly highlighting commercial fishing activities as an active vector. Furthermore, considering that the species was recorded within a marine protected area and deeper environments, these results highlight a potential ecological threat to local benthic ecosystems, emphasizing the urgent need f or competent authorities to implement spatiotemporal monitoring and public awareness campaigns to prevent the definitive establishment of this invader.

Chinese Bahaba (Bahaba taipingensis, Sciaenidae) is a Critically Endangered, Grade I state-protected marine fish in China. Reliable, non-invasive monitoring tools are urgently needed to inform conservation and restocking efforts. We developed and validated three TaqMan probe-based qPCR assays targeting mitochondrial 12S rRNA, ND5, and control region (D-loop) loci for species-specific detection of B. taipingensis. Primer-probe sets were designed from complete mitochondrial genomes and evaluated in silico against GenBank and in vitro against tissue DNA from B. taipingensis and closely related sciaenids, plus positive eDNA samples; sensitivity was quantified using serial dilutions of synthetic target DNA. All three assays showed high specificity and consistent amplification; 12S rRNA assay (Bhb_12S) was selected for field screening based on superior low-copy sensitivity and minimal by-products. We applied the Bhb_12S assay to 414 seawater samples collected from 23 sites in western Hong Kong during 2025 surveys, detecting B. taipingensis eDNA in the September samples (0.71-2.85 copies per L; mean 2.05), with positive detections confirmed by Sanger sequencing. Overall, these validated qPCR assays provide a robust molecular toolkit for non-invasive monitoring of B. taipingensis and will aid conservation planning, restocking evaluation, and long-term biodiversity assessments in the Pearl River Estuary and adjacent coastal waters.

The impact of invasive species on marine ecosystems is rapidly increasing, where they often outcompete native species in the absence of natural enemies. The parasite release hypothesis states that the success of invasive species relates partly to the loss of natural parasites during introduction and lower susceptibility to native parasites. Barnacles are highly successful invaders due to broad environmental tolerance and dispersal via shipping, but whether parasite release also participates in this success remains unknown. In this study, we analyse parasite infection patterns in native and invasive barnacles in the Wadden Sea by surveying communities across tidal zones. Additionally, year-round molecular monitoring of larval stages and a literature review were used to track the distribution of the invasive Pacific barnacle Balanus glandula in Europe and document its appearance in the Wadden Sea. The long-established invasive Austrominius modestus dominated the high and middle intertidal zone, whereas native species (Balanus crenatus and Amphibalanus improvisus) prevailed in lower zones. Native and invasive barnacles differed in parasite infection frequency (mostly cestodes and trematodes). The native Semibalanus balanoides had the highest prevalence (27%), followed by the invasive A. modestus (11%), and no infections were found in B. glandula. Lower parasite prevalence in invasive barnacles is consistent with the hypothesis that parasite release supports invasion success. In the absence of competent parasites, B. glandula could impact native barnacles through competition. Continued monitoring of B. glandula is recommended to track its distribution, interactions with native species, and parasite acquisition, providing further insight into the parasite release hypothesis.

Habitat degradation and biodiversity loss in the Black and Azov Seas necessitate improved tools for spatially explicit conservation planning. We employed stacked species distribution modelling (SSDM) to assess habitat quality for the three resident cetacean species, the common dolphin (Delphinus delphis ponticus), the bottlenose dolphin (Tursiops truncatus ponticus), and the harbour porpoise (Phocoena phocoena relicta), which serve as apex predators and indicators of ecosystem health. Occurrence data were compiled from the Global Biodiversity Information Facility (GBIF), and ensemble species distribution models (ESDMs) were constructed using nine algorithms within the SSDM framework, with eight environmental predictors extracted from Bio-ORACLE v3.0. Individual ESDMs demonstrated excellent predictive performance (AUC: from 0.82 to 0.83; TSS: from 0.65 to 0.67; prop.correct: from 0.82 to 0.83). However, the initial continuous stacking method (pSSDM) yielded low community-level prediction success (0.36), prompting evaluation of three correction approaches. The Probability Ranking Rule (PRR) substantially improved performance (prediction.success = 0.459, sensitivity = 0.704, Jaccard = 0.465), effectively mitigating the overprediction bias inherent in stacked models. Species richness mapping identified multi-species hotspots along the southwestern Black Sea shelf, the Crimean coast, the Kerch Strait, and parts of the eastern coast, while the deep central basin exhibited the lowest richness. Variable importance ranking revealed bathymetry as the primary community-level driver (41.2%), followed by dissolved oxygen (13.8%), sea surface temperature (11.9%), and salinity (10.4%). Species-specific importance patterns confirmed ecological niche segregation, with common dolphins favouring deeper offshore waters and bottlenose dolphins and harbour porpoises associated with shallower shelf environments. The moderate richness observed in the highly productive northwestern shelf, despite high nutrient inputs, may reflect a combination of natural factors (elevated turbidity, reduced salinity) and anthropogenic pressures (fisheries bycatch, shipping, coastal development, and military activity) that limit species co-occurrence. Our findings demonstrate that PRR-corrected SSDM provides a robust framework for mapping cetacean habitat quality and identifying conservation priorities in the Black and Azov Seas, offering an evidence-based tool to inform ecosystem-based management in this ecologically unique and increasingly pressured marine region.

Context Pumping stations pose a threat to fish globally through land use change, habitat fragmentation and entrainment risk, with the catadromous and critically endangered European eel particularly impacted. Objectives/methods Establish, model, assess and understand the present-day distribution of European eel and resident fishes in 152 pumping station catchments in a once extensive wetland (The Fens) using eDNA metabarcoding (855 samples over two and half years), with specific focus on anthropogenic influences on hydrological connectivity and habitat quality. A removal survey design maximised confidence in negative results while minimising time and consumable costs. Results Eel occurrence upstream of pumping stations was low (occupancy = 28.3%) and positively associated with catchment area, fish species richness and natural hydrological connectivity (gravity drainage or flooding) and negatively associated with distance from the tidal limit. Fish species richness replaced catchment area and improved model performance, potentially acting as a biotic indicator of habitat quality and connectivity. Pumped catchments with manually operated upstream water transfers had reduced eel presence, potentially linked to the direction of water flow or the timing of operation. By contrast, fish species richness increased in these catchments during summer, suggesting displacement into unsuitable long-term habitats. Physical habitat maintenance had no detectable effect on eel occurrence or fish species richness. Conclusions This study provides the first landscape-scale assessment of European eel distribution and drivers of occurrence in pumped river catchments. The highly novel and comprehensive insights have implications for European eel conservation as well as infrastructure and catchment management, including compliance with legislation (EC Regulation No. 1100/2007).

Knowledge regarding variation in habitat use among individuals is crucial for understanding population dynamics and for management and conservation measures. This is especially important for diadromous fishes that shift between habitats, being affected by external pressures and environmental change in different habitats over ontogeny. Herer, we assessed individual variation in habitat use of European eel along a salinity gradient, ranging from fully marine to freshwater in northern Europe, using otolith microchemistry data from >3600 eel together with established time-series segmentation and clustering methods. We show that eel display high degree of individual variation in habitat use. Assigned life-histories included coastal resident, freshwater resident, and coastal and freshwater habitat shifting individuals. Coastal resident eels were observed in a large range of salinities. Given the widespread occurrence of migration barriers in freshwater, it is unknown whether the coastal resident eel preferred that habitat, or if it was the only available habitat for them. Our findings nonetheless highlight the need to include coastal habitats when assessing population development and silver eel production of the critically endangered European eel.

Octocoral colonies with unusual morphology were detected in September 2022 and October 2023 in two coastal areas east of Havana, Cuba, and tentatively identified as Unomia stolonifera. U. stolonifera is an invasive octocoral from the Indo-Pacific that was first reported in the Caribbean off Venezuela in the 2000s, where it has spread rapidly, smothering coral reefs and substantially altering benthic communities. After obtaining tissue samples from a Cuban octocoral colony, we re-examined the specimen using molecular barcoding of three mitochondrial regions (16S/ND2, mtMutS, COI) and the nuclear large ribosomal subunit (28S rRNA), and we unequivocally identified it as Xenia umbellata. X. umbellata, a native of the Red Sea, was first identified in southern Puerto Rico in October 2023 and has since been found in various marine ecosystems along the southern coast of the island. The presence of either invasive octocoral species in Cuba or elsewhere in the Caribbean would be of a serious environmental concern due to their documented tolerance, totipotentiality, propagation capacity and significant negative interactions with local benthic fauna. Attempts to eradicate the invasive soft coral colonies from Cuban waters have been initiated with apparent success, helping to control further expansion. The most likely introduction pathway is the accidental or intentional releases from the aquarium trade but transport via ballast water cannot be ruled out. We cannot discount the possibility of independent invasion events from different routes to Puerto Rico and Cuba occurring within a year of each other. Propagation from Cuba to Puerto Rico, or vice versa, which we consider highly improbable, would likely imply that soft coral populations may also have been established on Hispaniola but have remained undetected in the Dominican Republic and Haiti to date.

Downstream migration and sea entry are periods of high mortality for sea trout smolts and migration timing is a critical aspect of survival. We aimed to investigate migration timing of PIT-tagged sea trout smolts across a latitudinal gradient in five freshwater systems across Europe: Norway, Sweden, Denmark, France and Portugal. In two systems, smolt migration was further examined to assess a) differences in sex, body size and condition between autumn and spring migrants; b) the influence of spatial origin within the stream; and c) relationships between individual body size and migration date. Tagged smolts were not detected migrating in the Portuguese watershed. Spring migration timing differed significantly between watersheds in Norway, Sweden, Denmark and France. Generally, there was a trend of earlier migration at lower latitudes. Autumn vs spring migration was examined in Gudso-Denmark. Autumn migrants were larger in both length and mass, with no differences in sex ratios or body condition. Fish originating from an upstream site were more likely to migrate in the autumn compared to the spring and vice versa. Size dependent migration was found in the Swedish system, Haga [a]-Sweden, with larger individuals migrating earlier in the spring than smaller individuals. Outward-migrating smolts were also more likely to originate from a downstream site than an upstream site. Overall, these results show both large-scale geographic and fine-scale individual influences on migration timing. Given that climate change may have large impacts on migration patterns in sea trout, understanding variability in migratory patterns across a latitudinal gradient is an important tool for predicting responses to environmental changes.

Capelin (Mallotus villosus), a key forage fish in the Northwest Atlantic, links zooplankton to predators including commercial fishes, seabirds, and marine mammals, yet its life-cycle movements in the Gulf of St. Lawrence (GSL) remain poorly understood. Between 2022 and 2024, otoliths from 927 individuals collected during and after spawning were analysed by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Building on previous work on regional structuring, seven trace elements (Li, B, Mg, K, Zn, Sr, Ba) were used to discriminate three regions. Early-life regional signatures were inferred through an edge-to-core approach, assigning otolith core chemistry to one of these regions using quadratic discriminant analysis. The core was treated as an integrated early-life signal (late-larval to early juvenile period) rather than a strictly natal signature. Spatial variation in core chemistry was consistent across cohorts, mirroring the stability documented on the otolith edge. Results revealed widespread dispersal alongside partial regional residency: individuals with northeastern early-life signatures showed the strongest correspondence between early-life and capture regions, whereas other regions were more connected. Fish sampled during spawning were more often reassigned to their inferred early-life region than post-spawning fish, a regional-scale homing-like pattern consistent with regional spawning fidelity. This coexistence of dispersive and resident strategies likely generates a portfolio effect buffering the population against environmental variability and localised reproductive failures.

Ranges of small benthic fauna are notoriously difficult to assess. In some of these cases, modern eDNA methods can shed light on species occurrence. Here we conduct an exploratory study on the fish eDNA recoverable from the gastrovascular cavities of the easy-to-sample pore water siphoning benthic invertebrate, Cassiopea, across six sites within the Florida Keys. Twenty-seven fish 12S identities were recovered from water samples, two from sediment samples, and seventeen from Cassiopea gut swabs. In total, thirty-two different species were identified from nineteen families, including one shark species (Ginglymostoma cirratum), and five species of cryptobenthic reef fishes (f: Gobiidae, Labrisomidae). Additionally, five species were identified from medusae samples that were not recovered in water or sediment samples. The species identities recovered may provide insight into the fish in direct proximity to Cassiopea assemblages, as well as indicate that Cassiopea may accrue disproportionate eDNA from cryptobenthic reef fish compared to surrounding environmental samples. The unorthodox sampling technique of using eDNA recovered from jellyfish stomachs yields another avenue for epibenthic community data acquisition.

BACKGROUNDOceanic islands and seamounts are recognised as hotspots of abundance and diversity for marine top predators, such as sharks and large teleosts, and are hypothesised to function as migratory stepping stones for mobile, pelagic species. However, while movements of pelagic predators between such features have been documented in some oceans, evidence from the tropical Atlantic remains limited. RESULTSHere, we report on long-distance migrations of three species of pelagic predator between oceanic islands and seamounts in the tropical south Atlantic recorded via independent passive acoustic telemetry arrays. These include the first recorded trans-Atlantic migration of a Galapagos shark (Carcharhinus galapagensis) from Ascension Island (UK) to the Sao Pedro and Sao Paul Archipelago (Brazil) (minimum distance 1,930 km); the longest documented oceanic migration of an Almaco jack (Seriola rivoliana) from St Helena (UK) to Ascension Island (minimum 1,300 km); and multiple movements of Galapagos and silky sharks (C. falciformis) between two Mid-Atlantic Ridge seamounts and Ascension Island (minimum 265-325 km). These detections are notable given the limited duration, sample sizes, and temporal overlap of acoustic tracking studies in the region, suggesting substantial connectivity across large spatial scales. CONCLUSIONSOur findings provide empirical support for the role of oceanic islands and seamounts as connectivity hubs for pelagic predators in the tropical Atlantic, underscoring their importance as key nodes in marine protected area networks. More broadly, this study demonstrates the value of collaborative regional tracking networks in resolving large-scale movement patterns and informing marine management at ecologically relevant scales.

The global coral reef crisis has prompted restoration initiatives worldwide. Targeting the coral larval stage is among the most scalable approaches as recruitment operates over large spatial scales. It thus represents one of the best levers for coral population recovery. Active coral larval seeding has shown considerable success, and passive substrate engineering has emerged as a promising complementary strategy. Coral settlement modules featuring helix recesses have increased settlement and survival by up to 80-fold on small experimental units, but whether these results translate to tools deployable at the scale of thousands of units, remains yet an open question. Here, we transferred structural features from successful experimental coral settlement designs into production-ready concrete modules to (i) evaluate coral recruitment on five designs at four reef sites differing in flow regime and coral cover over one year; (ii) compare production-scale performance against experimental clay modules and natural reef substrate; and (iii) identify key parameters for large-scale production. The helix recess geometry of coral settlement modules outperformed the featureless control design approximately 20-fold and exceeded natural reef recruitment at least 3- to 32-fold. The helix features were successfully transferred from experimental clay to production-scale concrete modules, yielding comparable settlement densities when standardized to crevice length, which proved to be the biologically relevant unit of available habitat. Production feasibility was demonstrated by producing 690 modules for deployment on a hybrid reef on the west side of Oahu, Hawaii. The passive coral larval recruitment approach presented here could substantially improve the logistical and economic feasibility of large-scale coral reef restoration. This approach requires neither coral larval rearing, handling, nor coral fragmenting, and is compatible with active larval seeding where genetic diversity or larvae supply are limiting factors. The coral settlement modules can be cast in standardized concrete molds at precast facilities. Modules have demonstrated consistent coral recruitment enhancement across reef environments with contrasting flow and coral cover. Deploying mixed arrays of helix-recess structures with designs offering multi-level complexity and three-dimensional rugosity maximizes outcomes for coral, fish, and invertebrate communities simultaneously. Site selection is the most critical deployment decision and should consider larval supply, hydrodynamics, and substrate stability which drive recruitment outcomes more than design choice alone. The modules offer a range of application potential, ranging from integration into existing coastal infrastructure over stand-alone reef restoration approaches, to substrate-consolidating interconnected arrangements.

Predicting bycatch patterns in tropical tuna purse seine fisheries remain challenging due to low variance explained by existing models, limiting their use for management purposes. To address this limitation, we combined ecological network analyses and community detection methods to characterize recurring bycatch assemblages in tropical tuna purse seine fisheries. Ecological network analyses consistently revealed two key bycatch communities: one dominated by bony fishes with low conservation concern, and another by IUCN-listed threatened species (NT-CR; sharks, rays, sea turtles). By focusing on sets with high numbers of threatened species, we identified bycatch hotspots near Mauritania, Gabon and Angola. These hotspots result from seasonal fishing patterns and specific bycatch compositions, with specific composition in terms of sex and age, compared to the rest of the Atlantic. We suggest that the Mauritanian region is a potential candidate for shark nursery and sea turtle foraging grounds. These insights can guide the development of bycatch reduction strategies based on predictable spatio-temporal or community-specific features and provide a basis for targeted management actions.

AimSeamounts are key components of deep-sea ecosystems. Yet, their biodiversity patterns and conservation needs remain poorly understood, presenting a critical knowledge gap as they face multiple environmental stressors. Here, we aim to characterize benthic community structure across multiple seamounts along the Kyushu-Palau Ridge (KPR) and identify conservation priorities. LocationPhilippine Sea in the Western Pacific. Major taxa studiedDeep-sea benthos. MethodsWe surveyed six transects (13.3{degrees}N-22.9{degrees}N; 614-5,055 m depth; 165 kilometers in total length) using a towed camera system, yielding 31,342 images and 14,218 identified individuals. Community structure was assessed through species depth-range overlap analysis to distinguish nestedness versus turnover patterns. {beta}-diversity was partitioned into local contributions (LCBD) and species contributions (SCBD) to evaluate site-level uniqueness and species-level influence. Generalized linear mixed models were used to relate LCBD and SCBD to depth, slope, aspect, bathymetric position, and functional traits. ResultsCommunity structures varied among slopes and seamounts. Western, steeper slopes were dominated by nestedness, whereas gentler eastern slopes showed mixed patterns of nestedness and gradual turnover. Sessile species largely exhibited nestedness, while mobile taxa showed mixed structures. LCBD declined with depth overall but increased on north-facing slopes and sites with higher broad-scale bathymetric position. Wide-ranging generalist species, particularly among Echinoidea and Holothuroidea, contributed disproportionately to {beta}-diversity. Main conclusionsSeamount benthic communities along the KPR are structured by interactions between depth, geomorphology, and species ecological breadth. The dominance of nestedness on western slopes suggests that protecting shallow, species-rich habitats could capture much of the biodiversity therein. In contrast, the mixed structures on eastern slopes indicate the need for a hybrid conservation approach that includes both shallow summits and deeper, compositionally distinct zones. Our findings highlight the importance of slope-specific, depth-informed strategies to conserve these vulnerable marine ecosystems.

The management of Atlantic bluefin tuna (Thunnus thynnus) is currently defined by a long-standing life-history paradox: a stark divergence in maturation schedules between the Eastern and Western stocks. While the Mediterranean contingent matures at approximately 104 cm straight fork length (SFL; age 3-5), the western stock has long been characterized as a late-maturing, at [~]190 cm SFL (age 8+), and as late as age 15.8, based on size-at-catch data in the presumed exclusive spawning areas of the Gulf of Mexico. This discrepancy defies maturity states confirmed by endocrine hormones as well as established life-history principles that link metabolic energetics to reproductive biology. To resolve this critical issue in stock assessment, we present a sensitivity analysis based on the first histological evidence of spawning- capable individuals from 42 bluefin females (97-244 cm curved fork length or [~]95- 236 cm SFL) sampled in June 2025 within the Slope Sea, Northwest Atlantic. This historically overlooked, temperate spawning ground must be recognized and past estimates of stock productivity reevaluated. Our data provide a conservative estimate of length-at-50% maturity, L50 for females at 123.3 cm SFL, effectively reconciling the reproductive parameters of the two stocks based on histology. Our findings align established bluefin tuna metabolic and evolutionary symmetries in life history, irrespective of management boundaries. Incorporating this previously unrecognized spawning group (i.e., smaller, younger fish) calls for a substantial upward revision of Western spawning stock biomass (SSB). This biomass represents an intrinsic biological buffer that could contribute to the Atlantic bluefins adaptation and resilience. Appreciating demographic diversity is critical to accurately diagnosing stock vulnerability, ensuring that management frameworks protect long-term population stability in the face of climate-driven oceanographic shifts and ongoing exploitation pressure.

This study investigates changes in habitat connectivity and meta-ecosystem resilience between 1817 and 2022 along a 150 km section of a large European river (Danube) and its adjacent floodplains. The analysis was based on a time series of functional habitat networks (graphs) constructed from historical records and remote sensing data, integrating habitat suitability and dispersal modes of functional organism groups. The results indicate that overall habitat availability declined by about 50% since 1817, leading to the near-complete loss of functional connectivity among dynamic habitats by 1910. Less dynamic habitats persisted or expanded but became functionally less connected. Connectivity-based habitat classification further revealed four distinct functional connectivity clusters and the near-complete loss of an originally dominant, dynamic, and highly connected habitat type. Furthermore, the results indicated a fundamental loss of meta-ecosystem resilience. This development was reflected by increased spatial modularity among functionally similar habitats and by reduced layer dissimilarity and structural robustness in multilayer networks representing the spatial habitat structure and functional habitat connectivity across different functional organism groups.